The installment — this season’s 15th — revolves around a wrestling tour rocked by some seriously scary mayhem. Among the colorful characters featured in the hour are “Gunnar Lawless,” a wrestling legend grappling with regrets, “Shawn Harley,” a quick-tempered and ambitious rookie on the rise, and “Rio,” a wrestling manager who is saddened to see so many of her guys meeting untimely ends.